1. Field of the Invention
The present invention relates to the field of liquid crystal displaying, and in particular to a TFT (Thin-Film Transistor) array substrate structure.
2. The Related Arts
Liquid crystal displays (LCDs) have a variety of advantages, such as thin device body, low power consumption, and being free of radiation, and are thus widely used, such as mobile phones, personal digital assistants (PDAs), digital cameras, computer monitors, and screens of notebook computers.
A liquid crystal display generally comprises an enclosure, a liquid crystal display panel arranged in the enclosure, and a backlight module mounted in the enclosure. As shown in FIG. 1, a conventional liquid crystal display panel comprises a TFT array substrate 100, a color filter (CF) substrate 300 located above and bonded to the TFT array substrate 100, a liquid crystal layer 500 arranged the array substrate 100 and the CF substrate 300, and a sealant frame 700 and the operation principle thereof is a drive voltage is applied between the TFT array substrate 100 and the CF substrate 300 to control liquid crystal molecules contained in the liquid crystal layer 500 to rotate so as to refract out the light from the backlight module to generate an image.
The liquid crystal display panels that are available in the main stream market can be classified in three categories according to the arrangement of the liquid crystal molecules, which are TN (twisted nematic)/STN (super twisted nematic), IPS (in-plane switching)/FFS (fringe field switching), and VA (Vertical Alignment), wherein the VA type liquid crystal display has advantages, such as high contrast, wide view angle, and excellent color displaying. However, the VA type display uses vertical rotation type liquid crystal, which shows color shift at a large view angle. A known solution for such a phenomenon is to divide a pixel zone into a main zone and a sub zone. Electrical voltage applied to opposite sides of liquid crystal is different for the main zone and the sub zone so that the rotation angle of the liquid crystal in the main zone and the sub zone is different thereby overcoming the color shift problem.
As shown in FIG. 2, which shows a schematic view of a conventional TFT (Thin-Film Transistor) array substrate structure used in a VA type liquid crystal display, the TFT array substrate structure comprises first and second gates 101, 103, a semiconductor layer 200 arranged on the first and second gates 101, 103, first and second sources 301, 303 arranged on the semiconductor layer 200, and first and second drains 402, 404 arranged on the semiconductor layer 200. The first and second gates 101, 103 are electrically connected. The first and second sources 301, 303 are electrically connected. The first gate 101 and the first drain 402 are arranged to overlap in space so as to form a first overlapping zone A and the first gate 101 has a first edge 105 corresponding to the first overlapping zone A and perpendicularly intersecting the first drain 402 in space. The second gate 103 and the second drain 404 are arranged to overlap in space so as to form a second overlapping zone B and the second gate 103 has a second edge 107 corresponding to the second overlapping zone B and perpendicularly intersecting the second drain 404 in space. A portion of the first drain 402 that corresponds to the first overlapping zone A and a portion of the second drain 404 that corresponds to the second overlapping zone B are each in the form of a strip, the two strips being arranged in directions that are perpendicular. The first source 301 is electrically connected to a data line; the first gate 101 is electrically connected to a gate scan line; and the first and second drains 402, 404 are respectively and electrically connected to a pixel electrode in a main zone and a sub zone. The first overlapping zone A induces a first parasitic capacitance and Cgs1 and the second overlapping zone B induces a second parasitic capacitance Cgs2. With the direction of strip of the first drain 402 being taken as a vertical direction, when the first and second drains 402, 404 moved relative to the first and second gates 101, 103 in the vertical direction, the first overlapping zone A undergoes a change of the area thereof, while the second overlapping zone B maintain constant the area thereof so that the first parasitic capacitance Cgs1 changes but the second parasitic capacitance Cgs2 does not.
According to the feed-through voltage formula:feed-through voltage ΔV=[Cgs/(Clc+Cs+Cgs)]×Vp-p 
where Clc is capacitance induced by a liquid crystal cell, Cs is storage capacitance, Cgs is the capacitance value of a parasitic capacitance induced between a gate and a drain, and Vp-p is voltage change of the gate.
It can be appreciated that the first feed-through voltage ΔV1 changes but the second feed-through voltage ΔV2 does not so that the voltage difference between is changed, making reference voltage VCOM for the rotation of liquid crystal molecules between the main zone and the sub zone changed.
Similarly, when the first and second drains 402, 404 are moved relative to the first and second gates 101, 103 in a horizontal direction, the area of the first overlapping zone A remains unchanged, but the area of the second overlapping zone B changes, so that the first parasitic capacitance Cgs1 does not change but the second parasitic capacitance Cgs2 changes, thereby making the first feed-through voltage ΔV1 not change but the second feed-through voltage ΔV2 changed, eventually leading to a change of VCOM.
Instability of VCOM would causes problems of flickering and image sticking occurring in a liquid crystal display panel thereby affecting the displaying quality. It is apparently desired to have further improvements over the known TFT array substrate structure.